The generic structure of a 4-quadrant phase interpolator as disclosed in the Applicant's prior patent no. GB2415101, is shown in FIG. 1, and consists of a set of 4 differential amplifiers driven by quadrature clocks Clk0 & Clk1 and their complements Clk2 & Clk3 (i.e. 4 quadrature phases in total). The four differential amplifiers effectively operate at 90° intervals and each is connected to a current source device whose bias voltage is controlled in order to adjust the phase of the outgoing clock to the desired alignment.
There is now a need for an improvement of the prior art 4-quadrant clock phase interpolator design to allow independent rotation of the output clocks in steps of 90°.